Hydrogen Terminated Silicon Nanopowders: Gas Phase Synthesis, Oxidation Behaviour, and Si-H Reactivity

Abstract

Silicon nanopowders were prepared by hot-wire chemical vapour deposition (CVD) from monosilane. Wire materials including Hf, Nb, Ta, Mo, W, Rh, Re, Ir, Pd, and Pt were tested. The filament temperature was varied in the range of 400 -2000°C and pressures between 1.0 -1.5 bar.Products were characterised by bulk elemental analysis and a laser granulometer. The powders were investigated by TG-DSC-MS under inert, O 2 , and H 2 O containing atmosphere, respectively, in a temperature range of 20 -700°C. Hydrogen evolution occurred in three separate steps, depending on the applied gas atmosphere. The oxidation mechanism was explored by the characteristic O x Si-H bands (x = 0 -3) observed in ex situ DRIFT experiments. The oxidation of hydrogen terminated silicon surfaces was investigated employing oxygen (O 2 ), hydrogen peroxide (H 2 O 2 ), permanganate (MnO − 4 ), or peroxodisulfate S 2 O 2− 8 in a temperature range of 0 -120°C. The oxidation was stepwise and strongly enhanced after pretreatment by alkyl lithium salts or Grignard reagents.

Oxidation of nanocrystalline silicon at room temperature and various humidity

“…Annealing has no effect on oxidation, but hydrosilated nc-Si are more resistant to oxidation. It was demonstrated that oxidation of nc-Si does not proceed in dry air or degassed water at room temperature [18], but the addition of moisture or oxygen respectively activates the process. Similar results were achieved for monocrystalline Si [11].…”